The formation of one or more microchannels on or within a substrate is useful for many different types of microfluidic applications, including micro analysis systems, micromechanical actuators, localized or global substrate cooling, and ink-jet printing. Micro analysis systems which utilize microminiature fluid channels include liquid and gas chromatography, electrophoresis, free-flow fractionation, and polmerase chain reaction.
Conventional methods for forming microchannels generally rely on the fabrication of the microchannels in a substrate, and then adhering or wafer bonding a cover plate over the substrate seal the microchannels (see e.g. U.S. Pat. No. 5,575,929 to Yu et al). Such conventional methods for forming microchannels can be problematic due to particulate contamination on the substrate or adhesive contamination in the microchannels. Furthermore, these conventional methods can require that the substrate be flat without any local or global warp. Finally, these conventional methods are generally not compatible with the formation of an integrated circuit on the substrate.
For many applications of microchannels, it is desirable to be able to form electronic circuitry on the same substrate as the microchannels. Such circuitry can be used to produce a flow of a particular fluid by electrokinetic pumping which can be used for separating specific components of the fluid (e.g. chromatographic or electrophoretic separation). Additionally, the provision of electronic circuitry on the substrate can be used for resistively heating the fluid, and/or for detection of specific components in the fluid for chemical analysis. Finally, electronic circuitry on the substrate can be used for signal processing, thereby forming a smart sensor.
Prior methods for forming microchannels on a substrate that are compatible with integrated circuit processing include the use of electroplated metals (see e.g. U.S. Pat. Nos. 5,871,158 and 5,876,582 to Frazier) and the deposition of various materials (e.g. silicon-carbon materials) by plasma enhanced chemical vapor deposition (see U.S. Pat. No. 5,783,452 to Jons et al).
An advantage of the present invention is that a process is disclosed whereby one or more hollow microchannels can be formed on or below a surface of a substrate, or both.
A further advantage of the present invention is that the microchannels can be fabricated using common clean-room techniques and equipment for compatibility with integrated circuit processing.
Yet another advantage of the present invention is that the microchannels can be formed at a low temperature less than 100.degree. C. and preferably near room temperature to eliminate detrimental effects to some materials (e.g. photoresist) used in forming the microchannels. The use of low temperature processes for forming the microchannels is also advantageous for compatibility with low-melting-point substrates (e.g. polymer substrates) or for certain metallizations (e.g. aluminum) on the substrate prior to forming the microchannels.
Yet another advantage of the present invention is that the microchannels can be formed completely lined with a silicon oxynitride material to present a uniform composition surface for fluid flow, thereby eliminating possible detrimental effects due to contact of the fluid with surfaces of different compositions, or with the substrate.
Still another advantage of the present invention is that the use of silicon oxynitride to form the microchannels produces microchannels which are electrically insulating for operation at high voltages as required for electrokinetic separations.
These and other advantages of the present invention will become evident to those skilled in the art.